Clarify English locale on filtering settings

We've applied this patch over on Catstodon/CatCatNya~, and are very grateful for its existence ^^

However, the description for the English locale is a bit unclear. I've clarified it a bit.

You should adjust the detail of "the regex pattern must be a single one" and "separate the blurhashes by newlines" in ja.yml separately, as it isn't specified there either.